Tyler did this when he was a puppy,and with razor sharp puppy teeth or needles it really hurts.

We used to let out a really loud ouch,scream say NO Biting etc and ignore him,no contact, sit on a chair with feet up till he calmed down.
Don't forget your puppy is probably starting to teeth,so he will need something hard to chew on,kongs are great with a filling inside,frozen carrots soothe sore gums too.